The advent of relatively inexpensive analog-to-digital (A/D) and digital-to-analog (D/A) converters and high density, high bandwidth recording media have made possible recording of high fidelity audio signals in digital format. An audio signal encoded into a digital signal can be recorded and processed without substantial loss of signal quality. That is, the signal may be encoded with error correction information so that the signal recovery system can recognize and correct errors in the recovered signal.
Recording and playback systems such as the video disc and video tape systems are readily adapted for recording and recovery of digital audio signals. Digital audio systems currently under development generally utilize these types of video systems, and, for purposes of time base correction of the signal recovered from the recording media, format the signal similar to a composite video signal. The encoded signal is grouped into sequential blocks separated by synchronization signals (similar to horizontal sync signals), the synchronization signals being utilized to monitor signal recovery speed and provide a means to adjust the record playback rate. In helical scan tape systems, signals similar to vertical blanking intervals are included to account for switching of the record/recovery tape head between signal tracks. Disc record systems on the other hand may have signal recorded on a single spiral convolution obviating track switching and the vertical blanking intervals. However, because of the extremely small dimensions of the signal track and signal recovery transducer, the transducer is susceptible of being ejected from the track by microdefects and/or particles in the track. Certain video disc systems provide track (convolution) identification numbers within the recorded information which are monitored to determine whether the transducer is properly tracking successive convolutions. If the transducer is anomalously translated a transducer steering mechanism returns it to the proper convolution.
Proper tracking of discs recorded with high quality digital audio is important because error correction for loss of signal from an entire convolution is impractical. Therefore track identification signals should be included in the recorded information to monitor the position of the pickup transducer. It is advantageous to divide each convolution into sectors and include track/convolution and sector identification to enable the recovery apparatus to quickly determine and correct anomalous pickup transducer positions.
Heretofore it was considered necessary to compress the digital audio signal manifestations to provide periodic intervals for the inclusion of track identification signal. This required inclusion of circuitry in the playback apparatus to subsequently remove the identification signal and expand the compressed audio signal into a time continuous signal. This generally requires a buffer memory having capacity to store the greater portion of the signal contained between successive identification numbers, significantly adding to the cost and complexity of the playback apparatus.